The present invention relates to impacting drills in general, and more particularly to impacting drills in which the impacting mechanism is selectively operatable.
There are already known various constructions of impacting drills, among them such which are equipped with an air cushion impacting mechanism and a tumbling mechanism that acts on the impacting mechanism to reciprocate the same in an adjustable manner during the operation of the impacting drill in the rotating and impacting mode. Conventional air cushion impacting mechanisms include an impacting element freely movable in the axial direction of the tool mounted in a chuck of the impacting drill, and a combination of a driving and a driven member which confine an air cushion between themselves. The tumbling mechanism then acts on the driving member to reciprocate the same in the axial direction of the tool and thus to impart impacts to the latter via the air cushion, the driven member, and the impacting element. The tumbling mechanism extends along a tumbling plane which revolves around an axis during the operation in the rotating and impacting mode and encloses an acute angle with such an axis. The adjustment of the operation is accomplished by varying the aforementioned acute angle.
An impacting drill of this type is known, for instance, from the published German patent application No. DE-OS 29 17 475. In this construction, the aforementioned driving member of the air cushion impacting mechanism is provided with a concentric annular groove and the tumbling mechanism includes a tumbling disc which has a peripheral portion that extends into such groove. The tumbling disc is mounted on an axially stationary shaft by means of a bolt extending transversely thereto, for pivoting about the axis of the bolt. A support disc having an inclined surface is mounted on the shaft at one axial side of the tumbling disc for joint rotation with the shaft but for displacement in the axial direction. The tumbling disc is pressed against the support disc by means of an axial compression spring which surrounds the shaft and is situated across the tumbling disc from the support disc. When the impacting drill is being used and is pressed by the user against a structure, a working cylinder of the impacting drill is displaced to a greater or lesser extent into the interior of the impacting drill, depending on the force with which the impacting drill or the tool thereof is being pressed against the structure. As a result of this displacement, the working cylinder abuts at the end face against the support disc and displaces the latter accordingly on the rotating shaft in dependence on the pressing force. This results in a change in the tumbling angle of the tumbling plane of the tumbling disc in dependence on the pressing force. Thus, a zero tumbling angle is obtained when the tool mounted in the impacting drill is disengaged from any structure to be drilled into, while a maximum tumbling angle results from the maximum pressing force.
The internal displacement of the working cylinder of this conventional impacting drill can be blocked by means of a shiftable switching arrangement having an internal abutment finger, thereby preventing displacement of the support disc out of the position corresponding to the zero tumbling angle and thus causing the impacting drill to operate in a so-called "impact-stop" mode, regardless of the pressing force.
Experience with the above-discussed construction of the impacting drill has shown that it has several drawbacks. Besides the problematical operative coupling between the tumbling disc and the working cylinder with the attendant play, noise, wear and reduced life span, this construction has an additional disadvantage which resides in the fact that the compression spring must fully accept the resulting mass and inertial forces. Accordingly, the compression spring must be made correspondingly strong, and so must the spring which restores the working cylinder into its initial position. The need for overcoming these spring forces results in a situation where the user must apply a relatively high force to the impacting drill when it is desired to operate in the rotating and impacting mode. Another disadvantage of this construction is that the adjustment of the tumbling angle is accomplished by means of the working cylinder of the air cushion impacting mechanism and its internal displacement, inasmuch as the axial dimension of the air cushion confined in the working cylinder becomes smaller with the increasing extent of the internal displacement, which runs contrary to the desired mode of operation of the air cushion impacting mechanism. When the latter is being operated with less than the maximum possible reciprocating stroke, all of the pressing force, which can be quite considerable under certain circumstances, is transmitted to the support disc. Consequently, the support disc is subjected to a high degree of wear. When the support disc is so mounted on the shaft that it can quite easily move in the axial direction, which would be favorable in terms of ease of handling of the impacting drill, there exists the danger that the support disc could become displaced in the axial direction of the shaft on its own, to thereby increase the reciprocating stroke beyond that corresponding to the pressing force.